‘Angelois’ (from ‘aggelos’) by itself is not a claim about the kind of being envisioned, but rather a claim about the function: a messenger
I think ‘seen by angels’ is a mistranslation, when we consider all that we know about the early apostolic confession.
In the Septuagint - the translation of the OT that the NT authors most frequently cited, it often simply means ‘messenger’, and a human one st that.
The word could easily refer to the apostles in 1 Tim 3:16. The translation ‘angels’ is not consistent with Paul's recognized common confession in 1 cor 15:3ff (1 Tim 3:16 greek= homologoumenōs is translated as ‘common confession’). I am almost certain that ‘angelon’ here simply means ‘messengers’(the connotation may be sent by God), just like in Galatians 4:14 ‘…hos angelon Theou’ = ‘…as a messenger from God’
1 Clement, writing to the Corinthian church that Paul founded, interprets this ‘common confession’ of the mystery along the same lines. That is human messengers/apostles - not angelic beings:
1 The Apostles received for us the gospel from our Lord Jesus Christ; our Lord Jesus Christ received it from God. 2 Christ, therefore, was sent out from God, and the Apostles from Christ; and both these things were done in good order, according to the will of God. 3 They, therefore, having received the promises, having been fully persuaded by the resurrection of our Lord Jesus Christ, and having been confirmed by the word of God, with the full persuasion of the Holy Spirit, went forth preaching the good tidings that the kingdom of God was at hand.
Note how Clements words to the Corinthians Linea up with 1 Timothy 3:16 and 1 Thess 1:
… and having been confirmed by the word of God, with the full persuasion of the Holy Spirit, went forth preaching the good tidings ...
1 Timothy 3:16
He appeared in the flesh,
was vindicated by the Spirit,
was seen by messengers,
was preached among the nations
1 Thess 1:5-7
because our gospel came to you not simply with words but also with power, with the Holy Spirit and deep conviction. You know how we lived among you for your sake. 6 You became imitators of us and of the Lord, for you welcomed the message in the midst of severe suffering with the joy given by the Holy Spirit.
Apostolic conviction of the truth of the Gospel by the spirit, by seeing it prefigured in the scriptures, was a Pauline emphasis already in his first letter, and Clement could expect the Corinthians to recognize this Pauline emphasis.
That is why I think angels is mistranslated in both Gal 4:4 and 1 Timothy 3:16.
Angelon in Paul ought to be translated as ‘messenger’ unless the context demands that we are talking about non-physical beings.
I am quite sure that angelon is not a claim about ontology - it is a claim about a divinely endorsed mission.